The present invention relates to a liner for a turbine section, said liner comprising a first wall, a plurality of webs interconnected with and projecting from said first wall, and a plurality of cooling channels, each of said cooling channels being delimited by two adjacent webs and said first wall, wherein each cooling channel presents a height corresponding to the height of its delimiting webs, and a width corresponding to the distance between its delimiting webs.
The invention also relates to a turbine section provided with the liner of the invention, a gas turbine engine provided with a turbine section according to the invention, and an aeroplane provided with a gas turbine engine according to the invention.
Preferably, the turbine section is a load-carrying frame arranged adjacent to at least one gas turbine, possibly but not necessarily located between two adjacent turbines, i.e. a high pressure turbine and a low pressure turbine. The load-carrying frame may be a so-called turbine centre frame, which may comprise an inner wall, an outer wall and a plurality of radial struts extending between said inner and outer walls. Said frame forms an annular channel, subdivided by said struts, through which the gases from an upstream combustion chamber passes, said gases thereby also passing the turbine or turbines of the engine. The liner according to the invention may comprise sheets or plates that are to be applied as a heat-protecting cover on the surface of any of said inner wall, outer wall and struts, said surface being a surface directed towards said annular channel.
Typically, the diameter of the gas turbine section of the invention will be in the range of one to two meters. However the invention may be applicable to corresponding gas turbine sections with dimensions outside said range.
A so called turbine centre frame of a turbine section of a gas turbine engine is often comprised by a load-Carrying part which is provided with sheets or plates that ensures the cooling thereof. These plates or sheets are not load-carrying, i.e. the load-carrying function and the cooling function are, mainly, divided on different parts of said section.
Normally, said plates or sheets comprise a first wall and a second wall divided and interconnected by longitudinal webs, said webs delimiting parallel channels between the first and second walls. The first wall is directed towards the channel through which hot gases are flowing through the turbine, while the second wall is directed towards the part to which the plate or sheet is attached.
A problem encountered by these plates is that their cooling ability is delimited due to inherent limitations of the structure thereof. Normally, cooling air is to be conducted through the channels of said plates, but there are limitations as to the amount of air that can be blown through the channels, and the pressure fall of the air in the channels also sets a limit to the cooling rate that may be achieved. Therefore, the plates become very hot, and, accordingly, they are conventionally made of a high temperature resistant material.
In order to lower the temperature of the plates, the heat flow through and out of the plates should be increased. Principally, there are only two possible ways accessible in order to achieve such a goal, namely either to improve the cooling, as for example achieved by means of the flow of cooling air, or to increase the heat conductibility of the plates.
Conventional solutions are based on the principle that cooling air drawn or blown through the channels of the plate are to absorb heat through convection from the wall adjacent to the hot combustion gases. However, since normally the delimitations of the engine do not permit a large flow of air of high velocity through the channels of the plates, it will not be easy to achieve the set target of lowering the wall temperature by increasing the cooling through the cooling medium in the channels.
It is desirable to present a liner as initially defined, the design of which is such that it presents an improved ability of conducting heat there through, such that, for a given temperature of the gases to which a first wall thereof is subjected during operation, the temperature of said first wall is decreased in relation to corresponding liners of prior art.
According to an aspect of the present invention, a liner is provided, characterised in that at least one of said cooling channels has a width/height ratio of below 5. The width/height ratio is markedly lower than what is common in prior art, as far as the applicant knows. By lowering said width/height ratio in relation to prior art, a larger proportion of the heat than before will be conducted to and through the webs, and a larger proportion of the heat than before will be transferred by means of convection from the webs to the cooling medium flowing through said channels during engine operation. Preferably, the liner comprises a plurality of parallel cooling channels, each delimited by two neighbouring webs, wherein a substantial part of said channels, preferably a majority thereof, and most preferably all of said channels present the width/height ratio. It is also preferred that both of the neighbouring webs that delimit said at least one cooling channel have substantially the same height. It is further preferred that at least the majority, and most preferably all of the webs present the same height, as measured in a direction perpendicularly from the surface of the first wall from which they project.
Preferably, the width/height ratio is below 3, even more preferably below 1, or, most preferably said ratio is below 0.5. It is also preferred that the width/height ratio is above 0.1.
Preferably, for said at least one channel, the ratio between the width of said at least one channel and the width of at least one of its delimiting webs is <2. Preferably, the width of said at least one channel and the width of each of its delimiting webs is <2. Among a plurality of parallel channels, these features are preferred for a substantial part thereof, preferably a major part thereof, and most preferably all of said channels.
According to a preferred embodiment, the width, or thickness, of each of said webs that delimit said at least one channel is below 2 mm. Preferably, among a plurality of such webs, a substantial part thereof, preferably a major part thereof, and most preferably all thereof present said width.
It is further preferred that the height of said at least one channel is above 2 mm., and preferably below 15 mm.
Preferably, the liner comprises a second wall interconnected with said first wall through at least some of said webs and located opposite to said first wall. Thereby, the liner present a number of separate cooling channels, each delimited by the first wall, the second wall and two neighbouring webs. Preferably, a substantial part of the webs, more preferably a major a part, and most preferably all of said webs interconnect said first and second walls, thereby being able to conduct heat from the first wall to the second wall, and also mechanically stabilising the liner.
The object of the invention is also achieved by means of the initially defined liner, characterised in that the material of the webs has a higher thermal conductivity than the material of the first wall. Thereby, a relatively larger proportion of heat than otherwise will be transferred through the webs, and, accordingly, a larger proportion of the heat will be transferred through convection from the webs to the cooling medium flowing through the channels of the liner. Preferably, such a design is combined with a liner design with the one or more of the features discussed herein.
According to a preferred embodiment, the material of the first wall has a higher temperature resistance than the material of the webs. Thereby, the ability of the liner to resist the immediate affection of hot gases flowing through turbine section in which the liner is positioned during operation may be provided for. The material of the webs can then be optimised with regard to other properties relevant for the function thereof, such as thermal conductivity.
Preferably, the material of the first wall comprises steel. Thereby, at least a layer of the first wall that is to be directly subjected and in contact with the hot gases flowing through the turbine section may, preferably, be made of steel, since the latter will provide acceptable mechanical as well as heat resistant properties.
Preferably, the material of the webs comprises copper or a copper alloy as a main constituent. Thereby an improved thermal conductivity of the webs is provided for.
According to an alternative embodiment, the material of the webs comprises a material the density of which is lower than that of the first wall. Since weight saving is an important issue in connection to the design of gas turbine engines to be used in vehicles, in particular aircrafts, a lighter material than that of the first wall might be preferred for the webs, especially since the number of webs and the total volume occupied thereby is likely to increase with a design in accordance with the invention.
According to a preferred embodiment the material of the webs comprises aluminium as a main constituent, due to an advantageous combination of light weight, high thermal conductivity, machinability, and availability of the latter. Depending on the cooling air conditions, aluminium alloys may be used in order to secure high temperature material properties while maintaining a higher conductivity and lower density than steel materials.
A mixture of copper and aluminium may be used, i.e. copper in the webs and aluminium in the outer wall or a part of the outer wall, i.e. the wall which is not facing the hot gases. In order to facilitate the use of aluminium, a thermal barrier coating (TBC coating) may be applied to the hot gas side.
The invention also includes a turbine section, characterised in that it comprises a liner according to the invention. Preferably, the liner is attached to a load-carrying part of said turbine section, whereby said part may be any of a radial strut connecting an inner wall and an outer wall of said turbine section, an inner wall of the turbine section, or an outer wall of the turbine section. Preferably, the first wall of the liner is turned towards the turbine chamber, such that it will be subjected to hot gases flowing therein during turbine operation.
Preferably, the turbine section comprises a load-carrying frame arranged adjacent to at least one gas turbine, normally a frame located between a low pressure turbine and a high pressure turbine as seen in the gas flow direction through the engine.
Further features and advantages of the present invention will be presented in the following detailed description.